Field of the Invention
Embodiments of the invention relate to an organic light emitting diode (OLED) display and a method for sensing device characteristics of the OLED display.
Discussion of the Related Art
An organic light emitting diode (OLED) display is a self-emission display device. The OLED display may be manufactured to have lower power consumption and a thinner profile than a liquid crystal display requiring a backlight unit. Further, the OLED display has advantages of a wide viewing angle and a fast response time. As the process technology of the OLED display has been developed to mass produce large-screens, the OLED display has expanded its market while competing with the liquid crystal display.
Each pixel of the OLED display includes an organic light emitting diode (OLED) having a self-emitting structure. The OLED display displays an input image using the OLED of the pixel that emits light when electrons and holes are combined in an organic layer through a current flowing in a fluorescence or phosphorescence organic thin film. An organic compound layer including a hole injection layer HIL, a hole transport layer HTL, an emission layer EML, an electron transport layer ETL, an electron injection layer EIL, etc. is stacked between an anode and a cathode of the OLED.
The OLED display may be variously classified depending on kinds of emission materials, an emission method, an emission structure, a driving method, and the like. For example, an OLED display may be classified into a fluorescent emission type and a phosphorescent emission type depending on the emission method. Further, the OLED display may be classified into a top emission type and a bottom emission type depending on the emission structure. Further, the OLED display may be classified into a passive matrix OLED (PMOLED) display and an active matrix OLED (AMOLED) display depending on the driving method.
Each pixel of the OLED display includes a driving thin film transistor (TFT) controlling a driving current flowing in the OLED depending on data of the input image. Device characteristics of the driving TFT (e.g., a threshold voltage and a mobility of the driving TFT) may change depending on a process deviation, a driving time, a driving environment, etc. The pixels of the OLED display are degraded due to changes in the device characteristics of the driving TFTs. The degradation of the pixels leads to an inferior image quality and decreased lifespan of the OLED display. Thus, technology for sensing changes in the device characteristics of the pixels and modify input data to the pixels based on the sensing result to compensate for the degradation of the pixels is used in the OLED display. The changes in the device characteristics of the pixels include changes in the characteristics of the driving TFT including the threshold voltage, the mobility, etc. of the driving TFT.
Because a related art compensation technology periodically senses changes in device characteristics of all of pixels so as to decide changes in device characteristics of each pixel, it takes a long time for the related art compensation technology to sense changes in the device characteristics of the pixels. Further, the related art compensation technology requires a mass memory capable of storing sensing data of all of the pixels.